JP7604903B2 - Heating unit - Google Patents

Description

The present invention relates to a heating unit used in a fixing device of an electrophotographic image forming apparatus.

Conventionally, a fixing device in which a rotating belt is sandwiched between a ceramic heater and a pressure roller is known (Patent Document 1). In this fixing device, the ceramic heater has a substrate and a resistance heating element, and a sheet-like heat conductive member is arranged in contact with the back surface opposite the nip surface that contacts the belt. A through hole is formed in the heat conductive member, and a temperature detection member contacts the back surface of the ceramic heater through this through hole.

JP 2017-194719 A

However, when a heater has a resistive heating element mounted on a substrate, there will be a difference in temperature between the area close to the resistive heating element and the area far from the resistive heating element. Therefore, if a temperature detection member is placed in direct contact with the rear surface of the heater, as in conventional technology, there is a possibility that the temperature will not be detected accurately due to the uneven temperature caused by the placement of the resistive heating element.

Therefore, the present invention aims to detect temperature accurately using a temperature detection component.

The heating unit for solving the above-mentioned problems includes a substrate, a resistive heating element supported on the substrate, a heater having a nip surface and a back surface opposite the nip surface, a temperature detection member for detecting the temperature of the heater, an endless belt having an inner surface in contact with the nip surface and rotating around the heater, a holder for supporting the heater, a sheet-like first heat conduction member located between the heater and the holder and having a thermal conductivity higher than that of the substrate, the first heat conduction member having a first heater side surface facing the heater side, a first opposite surface opposite the first heater side surface, and an opening, and a sheet-like second heat conduction member arranged at a position corresponding to at least the opening when viewed from an orthogonal direction perpendicular to the first opposite surface, the second heat conduction member having a second heater side surface facing the heater side and a second opposite surface opposite the second heater side surface.
The temperature sensing member is in contact with the second opposite surface of the second thermally conductive member.

With this configuration, the temperature detection member does not directly contact the rear side of the heater, but contacts the second opposite side of a second heat conduction member that is separate from the first heat conduction member. This averages out temperature variations caused by the placement of the resistive heating element, allowing the temperature detection member to detect an accurate temperature.

It is desirable that the thermal conductivity from the heater to the second opposite surface be better than the thermal conductivity from the heater to the first opposite surface.

This configuration allows the temperature detection element to detect the temperature accurately while ensuring the responsiveness of the temperature detection element to the heater temperature.

The thermal conductivity of the second thermal conductive member may be greater than the thermal conductivity of the first thermal conductive member. Also, the thickness of the second thermal conductive member may be less than the thickness of the first thermal conductive member.

This configuration ensures the responsiveness of the temperature detection element to the heater temperature while allowing the temperature detection element to accurately detect the temperature.

When viewed from the orthogonal direction, the size of the second heat conducting member may be smaller than the size of the first heat conducting member.

The second thermally conductive member may also be located within the opening.

In the longitudinal direction of the heater, the length of the first thermally conductive member may be longer than the length of the resistive heating element.

This configuration allows the heater temperature to be uniform throughout the entire area in the longitudinal direction of the heater where the resistive heating element is located.

The temperature detection member may be positioned in the longitudinal direction of the heater so as to detect the temperature at a position within a range through which a recording material of the maximum width usable by the heating unit can pass, and outside a range through which a recording material of the minimum width usable by the heating unit can pass.

With this configuration, the temperature detection member can detect the temperature rise in the area where the smallest width sheet does not pass through.

The first thermally conductive member may be made of aluminum or an aluminum alloy.

The first thermally conductive member may be an anisotropic thermally conductive member having a thermal conductivity greater in a direction parallel to the first heater side surface than in a direction perpendicular to the first heater side surface.

The heating unit may further include a sheet-like third heat conducting member having a third heater side that contacts the back side of the heater and a third opposite side opposite the third heater side. In this case, the first heat conducting member may have the first heater side in contact with the third opposite side, and the second heat conducting member may have the second heater side in contact with the third opposite side.

The third heat conducting member may be an anisotropic heat conducting member having a higher thermal conductivity in a direction parallel to the third heater side surface than in a direction perpendicular to the third heater side surface.

The anisotropic heat conductive member is, for example, a graphite sheet.

The second thermally conductive member may be made of aluminum or an aluminum alloy.

The temperature detection member may have a protrusion, and the second heat conduction member may be engaged with the protrusion and positioned relative to the temperature detection member.

This configuration allows the second thermal conductive member to be appropriately positioned relative to the temperature detection member.

The second thermally conductive member may have a protrusion, and the protrusion may be engaged with the temperature detection member to position the second thermally conductive member relative to the temperature detection member.

This configuration allows the second thermal conductive member to be appropriately positioned relative to the temperature detection member.

The temperature detection member may be a thermistor or a current interruption member that cuts off the flow of electricity to the resistive heating element if the heater becomes abnormally hot.

According to the present invention, the temperature detection member can detect the temperature accurately.

FIG. 2 is a cross-sectional view of the heating unit at the location of the thermistor. FIG. 3A shows the surface on which the resistive heating element of the heater is arranged, FIG. 3B shows the heater, the first thermal conductive member and the second thermal conductive member as viewed from the back side of the heater, and FIG. 3C shows the holder as viewed from the opposite side to the heater. 2A is a perspective view of a thermistor, and FIG. 2B is a perspective view of a current interrupting member. 4 is a cross-sectional view of the heating unit at the position of the current interrupting member. FIG. 1A is a cross-sectional view along the longitudinal direction of the heating unit, explaining the positioning of the second heat conductive member and thermistor, and FIG. 1B is a cross-sectional view along the longitudinal direction of the heating unit, explaining the positioning of the second heat conductive member and the current interrupting member. 11 is a cross-sectional view of a heating unit when a second heat conducting member is larger than the opening. FIG. 13 is a cross-sectional view of a heating unit including a third heat conductive member. FIG. 13 is a cross-sectional view of a heating unit according to a modified example in which the second heat conducting member is thinner than the first heat conducting member. FIG. FIG. 1A is a cross-sectional view along the longitudinal direction of the heating unit illustrating another embodiment of the positioning of the second heat conductive member and thermistor; FIG. 1B is a cross-sectional view along the longitudinal direction of the heating unit illustrating another embodiment of the positioning of the second heat conductive member and the current interruption member; and FIG. 1C is an enlarged cross-sectional view along the longitudinal direction of the heating unit illustrating yet another embodiment of the positioning of the second heat conductive member and thermistor. FIG. 1A shows the surface on which the resistive heating element of a modified heater is arranged, FIG. 1B shows the heater, the first thermal conductive member and the second thermal conductive member as viewed from the back side of the heater, and FIG. 1C shows the holder as viewed from the opposite side to the heater.

The heating unit 1 according to the embodiment is used in a fixing device of an image forming apparatus, a device for transferring foil by heat, etc. As shown in FIG. 1, the heating unit 1 includes a belt 3, a heater 10, a holder 20, a first heat conducting member 30, a second heat conducting member 45, 46 (see FIG. 4), a thermistor 50 as an example of a temperature detecting member, and a current interrupting member 60 as another example of a temperature detecting member (see FIG. 4).

The belt 3 is endless and made of metal or resin. The belt 3 rotates around the heater 10 while being guided by the holder 20. The belt 3 has an outer peripheral surface and an inner peripheral surface. The outer peripheral surface comes into contact with the sheet to be heated. The inner peripheral surface comes into contact with the heater 10.

The heater 10 has a substrate 11, a resistance heating element 12 supported by the substrate 11, and a cover 13. The substrate 11 is a long and narrow rectangular ceramic plate. The heater 10 is a so-called ceramic heater. The resistance heating element 12 is formed by printing on one side of the substrate 11. As shown in FIG. 2(a), in this embodiment, two resistance heating elements 12 are provided. The two resistance heating elements 12 are each long in the longitudinal direction of the heater 10 (hereinafter, the longitudinal direction of the heater 10 is simply referred to as the "longitudinal direction") and are arranged parallel to each other and spaced apart from each other in the lateral direction perpendicular to the longitudinal direction. A conductor 19A is connected to one end 12A of each resistance heating element 12, and a terminal 18 for supplying power is provided at each end of the conductor 19A. The other ends 12B of each resistance heating element 12 are connected to each other by the conductor 19B. The number of resistance heating elements 12 is not particularly limited. It is also possible to provide a resistive heating element in which the heat generation amount at the longitudinal center is greater than the heat generation amount at the longitudinal ends, and a resistive heating element in which the heat generation amount at the longitudinal ends is greater than the heat generation amount at the longitudinal center, and to adjust the heat generation distribution in the longitudinal direction by controlling each resistive heating element individually.

The cover 13 covers the resistance heating element 12. The cover 13 is made of, for example, glass. The heater 10 has a nip surface 15 that contacts the inner peripheral surface of the belt 3, and a back surface 16 on the opposite side to the nip surface 15.

The holder 20 is a member that supports the heater 10. The holder 20 has a support portion 21 and a guide portion 22. The support portion 21 has a plate shape corresponding to the shape of the heater 10. The support portion 21 has a support surface 21A that faces the side where the heater 10 is arranged, and an inner surface 21B opposite to the support surface 21A. As shown in FIG. 2(c), the support portion 21 has holder openings 25A, 25B, and 26 that penetrate the support portion 21. The holder opening 25A is disposed in the center of the support portion 21 in the longitudinal direction, and is a rectangle that is long in the longitudinal direction. The holder opening 26 is disposed at one end of the support portion 21 in the longitudinal direction, and is a rectangle that is long in the longitudinal direction. The holder opening 25B is disposed at the other end of the support portion 21 in the longitudinal direction, and is a rectangle that is long in the longitudinal direction.

The thermistor 50 includes two thermistors, a first thermistor 50A and a second thermistor 50B. The first thermistor 50A and the second thermistor 50B are the same part. The first thermistor 50A detects the temperature of the center of the heater 10 in the longitudinal direction. The first thermistor 50A is used to control the temperature of the heater 10 to a target temperature based on the temperature detected by the first thermistor 50A. The second thermistor 50B detects the temperature of the heater 10 at a position closer to the end of the heater 10 than the position detected by the first thermistor 50A in the longitudinal direction of the heater 10. The second thermistor 50B is used to detect that the temperature has increased at a position closer to the end of the heater 10. The holder opening 25A is disposed at a position corresponding to the first thermistor 50A. The first thermistor 50A and the second thermistor 50B do not have to be the same part. In this case, it is desirable for the first thermistor 50A to be a material that has higher temperature detection accuracy than the second thermistor 50B within the temperature range during printing operations.

The current interrupting member 60 is a member that cuts off the flow of electricity to the resistance heating element 12 when the heater 10 becomes abnormally hot. The holder opening 26 is positioned at a position corresponding to the current interrupting member 60.

Returning to FIG. 1, the guide portions 22 are provided at both ends of the support portion 21 in the short direction. Each guide portion 22 has a guide surface 22G that runs along the inner peripheral surface of the belt 3. As shown in FIG. 1 and FIG. 2(c), the guide portion 22 has a plurality of guide ribs 22A aligned in the longitudinal direction.

The first heat conducting member 30 is a member for conducting heat in the longitudinal direction of the heater 10 to make the temperature of the heater 10 uniform in the longitudinal direction. The first heat conducting member 30 is a sheet-like member and is positioned between the heater 10 and the support part 21 of the holder 20. When the heating unit 1 sandwiches a sheet, which is an object to be heated, between itself and another pressure member, the first heat conducting member 30 is sandwiched between the heater 10 and the support part 21. The first heat conducting member 30 has a first heater side surface 31 that contacts the back side surface 16 of the heater 10, and a first opposite surface 32 opposite the first heater side surface 31. The first opposite surface 32 is in contact with the support surface 21A of the support part 21.

2B, the first thermal conductive member 30 has first openings 35A and 35B as an example of an opening penetrating the first thermal conductive member 30, and a second opening 36 as another example of an opening. The first opening 35A is disposed in the center of the first thermal conductive member 30 in the longitudinal direction, and has a rectangular shape that is long in the longitudinal direction. The first opening 35A is disposed at a position corresponding to the holder opening 25A, that is, at a position corresponding to the first thermistor 50A.
The second opening 36 is disposed at one end of the first heat conductive member 30 in the longitudinal direction, and has a rectangular shape that is long in the longitudinal direction. The second opening 36 is disposed at a position corresponding to the holder opening 26, that is, at a position corresponding to the current interruption member 60.
The first opening 35B is disposed at the other end of the first thermal conductive member 30 in the longitudinal direction, and has a rectangular shape that is long in the longitudinal direction. The first opening 35B is disposed at a position corresponding to the holder opening 25B, that is, at a position corresponding to the second thermistor 50B.

1, the first heat conducting member 30 is a member whose thermal conductivity in a direction parallel to the first heater side surface 31 (hereinafter simply referred to as the "planar direction") is greater than the thermal conductivity in the planar direction of the substrate 11. The material of the first heat conducting member 30 is not particularly limited, but metals with high thermal conductivity such as aluminum, aluminum alloys, and copper can be used. The first heat conducting member 30 may also be an anisotropic heat conducting member whose thermal conductivity in the planar direction is greater than the thermal conductivity in the thickness direction perpendicular to the first heater side surface 31. For example, a graphite sheet can be used as the anisotropic heat conducting member. The thickness of the first heat conducting member 30 is also not particularly limited, and may be, for example, a film-like member thinner than 0.1 mm, or a plate-like member thicker than 1 mm.

The second thermal conduction members 45, 46 are intended to conduct heat in a planar direction to uniformly change the temperature of the portions where the second thermal conduction members 45, 46 are in contact with the heater 10, and to quickly transfer heat from the heater 10 to the temperature detection member (thermistor 50 or current interruption member 60).
The second thermally conductive member 45 is a sheet-like member and has a second heater side surface 45F facing the heater 10 side, and a second opposing surface 45R opposite to the second heater side surface 45F.
As shown in FIG. 4, second thermal conductive member 46 similarly has a second heater side surface 46F facing the heater 10 and a second opposing surface 46R opposite to second heater side surface 46F.

1 and 4, second thermal conduction members 45, 46 are disposed at positions corresponding to first openings 35A, 35B and second opening 36 when viewed from a direction perpendicular to first opposite surface 32 of first thermal conduction member 30. Second thermal conduction member 45 includes second thermal conduction member 45A and second thermal conduction member 45B. In this embodiment, second thermal conduction member 45A and second thermal conduction member 45B are the same component, except that they are disposed at different positions.
In this embodiment, the size of the second thermal conductive members 45A, 45B, 46 is smaller than the first thermal conductive member 30. The second thermal conductive member 45A is located in the first opening 35A. The second thermal conductive member 45B is located in the first opening 35B. The second thermal conductive member 46 is located in the second opening 36.

The second heat conducting members 45, 46 are members whose thermal conductivity in a planar direction is greater than that of the substrate 11 in the planar direction. The material of the second heat conducting members 45, 46 is not particularly limited, but metals with high thermal conductivity, such as aluminum, aluminum alloys, and copper, can be used. The thickness of the second heat conducting members 45, 46 is not particularly limited, and may be, for example, a film-like member thinner than 0.1 mm, or a plate-like member thicker than 1 mm.

The size of the second heat conducting members 45, 46 in the short side direction perpendicular to the longitudinal direction is larger than the size of the resistance heating element 12 in the short side direction. In this embodiment, the second heat conducting members 45, 46 are located between the two resistance heating elements 12 in the short side direction.

The second heat conducting members 45, 46 have better thermal conductivity at least in the thickness direction than the first heat conducting member 30. Therefore, the thermal conductivity from the heater 10 to the second opposite surface 45R, 46R is better than the thermal conductivity from the heater 10 to the first opposite surface 32. Good thermal conductivity here does not only mean that the thermal conductivity of the material of the second heat conducting members 45, 46 is high, but also means that heat is transferred quickly including the thickness of the second heat conducting members 45, 56. For example, as shown in Figures 1 and 4, when the first heat conducting member 30 and the second heat conducting members 45, 46 have the same thickness, if the thermal conductivity of the second heat conducting members 45, 46 in the thickness direction is higher than the thermal conductivity of the first heat conducting member 30 in the thickness direction, heat is transferred faster from the heater 10 to the second opposite surface 45R, 46R than from the heater 10 to the first opposite surface 32. Furthermore, if the first heat conducting member 30 and the second heat conducting member 45 are made of the same material and have the same thermal conductivity, and the thickness of the second heat conducting member 45 is smaller than the thickness of the first heat conducting member 30 as in the modified example shown in FIG. 8, heat is transferred faster from the heater 10 to the second opposite surface 45R, 46R than from the heater 10 to the first opposite surface 32.

As shown in FIG. 5(b), the second heat conducting member 46 has a protrusion 46B that protrudes in the thickness direction toward the current interrupting member 60. The protrusion 46B protrudes from the end of the second heat conducting member 46 in the longitudinal direction.

As shown in FIG. 3(b), the thermistor 50 (50A, 50B) has a support plate 51, a biasing member 52, a film 53, and a temperature detection element 55. The biasing member 52 is a sponge-like elastic member supported by the support plate 51. The biasing member 52 has a D-shaped cross section. The temperature detection element 55 is disposed so as to be located at the most protruding portion of the biasing member 52, and is connected to wiring (not shown). The film 53 is disposed so that the temperature detection element 55 is located at the most protruding portion of the biasing member 52, and is attached to the support plate 51 by being wrapped around the biasing member 52 and the support plate 51.

As shown in FIG. 3(a), the film 53 has slits 53X at both ends in the longitudinal direction that extend in a direction perpendicular to the longitudinal direction. Therefore, the film 53 has a central portion 53A located in the longitudinal center and in contact with the biasing member 52, and protruding portions 53B located at both ends in the longitudinal direction. As shown in FIG. 5(a), when the thermistor 50 is attached to the holder 20 and pressed against the second heat conducting members 45A and 45B, the biasing member 52 is crushed, and the protruding portions 53B are portions that protrude relative to the central portion 53A. The second heat conducting members 45A and 45B are positioned relative to the thermistor 50 by engaging the protruding portions 53B at both longitudinal ends.

As shown in FIG. 3(b), the current interrupting member 60 is a thermostat with a bimetallic interrupting mechanism inside, and has a case 61 that houses the interrupting mechanism, and a detection part 62 that detects temperature and protrudes from the case 61. As shown in FIG. 5(b), the second heat conducting member 46 is positioned relative to the current interrupting member 60 by the protrusions 46B engaging with both longitudinal ends of the detection part 62.

As shown in FIG. 1, the portion of the first thermistor 50A that protrudes from the support plate 51 enters the holder opening 25A and contacts the second opposite surface 45R of the second heat conductive member 45A through the holder opening 25A. The biasing member 52 of the first thermistor 50A is crushed, and the temperature detection element 55 is pressed against the second opposite surface 45R of the second heat conductive member 45A. The configuration in which the second thermistor 50B contacts the second opposite surface 45R is the same as the configuration in which the first thermistor 50A contacts the second opposite surface 45R, so a description thereof will be omitted.

The first openings 35A, 35B are preferably as small as possible to accommodate the second heat conductive members 45A, 45B. For example, the longitudinal size of the first openings 35A, 35B is preferably 1.5 times or less than the longitudinal size of the second heat conductive members 45A, 45B. The transverse size of the first openings 35A, 35B is preferably 1.5 times or less than the transverse size of the second heat conductive members 45A, 45B. The planar size of the second heat conductive members 45A, 45B is, for example, the same size as the biasing member 52. Preferably, the transverse size of the second heat conductive members 45A, 45B is greater than the width of one resistive heating element 12 and greater than the spacing between adjacent resistive heating elements 12.

As shown in FIG. 4 , the current interrupting member 60 has a detection portion 62 protruding from a case 61 that fits into the holder opening 26 and contacts the second opposite surface 46R of the second heat conducting member 46 through the holder opening 26 .
The second opening 36 is preferably as small as possible so that the second heat conductive member 46 can be disposed therein. For example, the size of the second opening 36 in the longitudinal direction is preferably 1.5 times or less the size of the second heat conductive member 46 in the longitudinal direction. The size of the second opening 36 in the lateral direction is preferably 1.5 times or less the size of the second heat conductive member 46 in the lateral direction. The size of the second heat conductive member 46 in the planar direction is, for example, equal to the size of the detection unit 62. Preferably, the second heat conductive member 46 is larger than the width of one resistive heating element 12 and larger than the interval between adjacent resistive heating elements 12 in the lateral direction.

2, the first thermistor 50A is positioned to detect the temperature at a position within the range through which a sheet of the minimum width W2 usable in the heating unit 1 can pass. The second thermistor 50B is positioned to detect the temperature at a position within the range through which a sheet of the maximum width W1 usable in the heating unit 1 can pass, and outside the range through which a sheet of the minimum width W2 usable in the heating unit 1 can pass (the range on the other end side where the second thermistor 50B can be placed is shown as end range AE1 in FIG. 2). The current interrupting member 60 is positioned to detect the temperature at a position within the range through which a sheet of the maximum width W1 usable in the heating unit 1 can pass, and outside the range through which a sheet of the minimum width W2 usable in the heating unit 1 can pass (the range on one end side where the current interrupting member 60 can be placed is shown as end range AE2 in FIG. 2).

One end 12A and the other end 12B of resistance heating element 12 are located outside maximum width W1 in the longitudinal direction and inside one end 38A and the other end 38B of first thermal conductive member 30. In other words, the length of first thermal conductive member 30 is longer than the length of resistance heating element 12 in the longitudinal direction.
Furthermore, one end 38A and the other end 38B of first thermal conductive member 30 are located, in the longitudinal direction, outside one end 12A and the other end 12B of resistance heating element 12 and inside one end 11A and the other end 11B of substrate 11. In other words, in the longitudinal direction, the length of substrate 11 is longer than the length of first thermal conductive member 30.

The effects of the heating unit 1 described above will now be described.
Thermistor 50 contacts second opposite surface 45R of second heat conductive member 45, and current interrupting member 60 contacts second opposite surface 46R of second heat conductive member 46. Second heat conductive members 45, 46 have better thermal conductivity in the thickness direction than first heat conductive member 30, so that thermistor 50 and current interrupting member 60 have good responsiveness to the temperature of heater 10.
On the other hand, if the thermistor 50 and the current interrupting member 60 were to directly contact the rear side surface 16 of the heater 10, they may be affected by temperature unevenness due to the arrangement of the resistance heating body 12. For example, if the thermistor 50 and the current interrupting member 60 were to contact a portion of the rear side surface 16 that corresponds to the area between the two resistance heating bodies 12 in the short direction, there is a possibility that the temperature cannot be detected accurately. However, in this embodiment, the thermistor 50 and the current interrupting member 60 do not directly contact the rear side surface 16 of the heater 10, but contact the second opposite surfaces 45R, 46R of the second heat conducting members 45, 46 that are separate from the first heat conducting member 30, so that the temperature unevenness due to the arrangement of the resistance heating body 12 can be averaged by the second heat conducting members 45, 46. This allows the thermistor 50 and the current interrupting member 60 to detect the temperature accurately.

The end ranges AE1 and AE2 are areas where the temperature is likely to rise when a sheet with a minimum width W2 is heated, because the heat is not taken away by the sheet with a minimum width W2. When the temperature of the end ranges AE1 and AE2 rises, the heat of the heater 10 flows from the end ranges AE1 and AE2 toward the inner range of the minimum width W2 through the first heat conductive member 30 and the second heat conductive members 45B and 46. If the second heat conductive members 45B and 46 were not present, heat would not be able to flow in the longitudinal direction in that area, but in this embodiment, the second heat conductive members 45B and 46 are present, so the thermal conductivity performance of the end ranges AE1 and AE2 is not significantly impaired. Therefore, the temperature rise at the longitudinal ends of the heater 10 can be suppressed.

In addition, the thermal conductivity from the heater 10 to the second opposite surface 46R is better than the thermal conductivity from the heater 10 to the first opposite surface 32, so the thermistor 50 and the current interrupting member 60 can detect the temperature accurately while ensuring the responsiveness of the thermistor 50 and the current interrupting member 60 to the temperature of the heater 10.

In addition, since the length of the first heat conducting member 30 is longer than the length of the resistive heating element 12, the temperature of the heater 10 can be made uniform throughout the entire range in which the resistive heating element 12 is disposed in the longitudinal direction of the heater 10.

The second thermistor 50B is positioned to detect the temperature at the position of the end range AE1, so that the second thermistor 50B can detect the temperature rise in the end range AE1.

The current interrupting member 60 is positioned to detect the temperature at the position of the end range AE2, so that the temperature rise in the end range AE2 can be detected by the current interrupting member 60.

The second heat conducting member 45 engages with the protrusion 53B of the thermistor 50, so that the second heat conducting member 45 can be appropriately positioned relative to the thermistor 50.

The protrusion 46B of the second heat conducting member 46 engages with the current interrupting member 60, so that the second heat conducting member 46 can be appropriately positioned relative to the current interrupting member 60.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate.

For example, as in the heating unit 1B shown in FIG. 6, the second heat conducting member 40 may be configured to be larger than the openings (first openings 35A, 35B) of the first heat conducting member 30. In this embodiment, the second heat conducting member 40 has the same size as the first heat conducting member 30 in the longitudinal direction or is larger than the first heat conducting member 30, and has the same size as the first heat conducting member 30 in the lateral direction. The second heat conducting member 40 has a second heater side surface 40F in contact with the rear side surface 16 of the heater 10, and a second opposite surface 40R in contact with the first heater side surface 31 of the first heat conducting member 30. Even in such a case, the second heat conducting member 40 is provided at a position corresponding to the first openings 35A, 35B, and a temperature detection member (such as a thermistor 50) is in contact with the second opposite surface 40R, so that the same effect as the above embodiment can be achieved.
In this embodiment, second thermal conductive member 40 may be, for example, a graphite sheet which is an anisotropic thermal conductive member.

Also, as in the heating unit 1C shown in FIG. 7, a sheet-like third heat conducting member 70 may be provided between the heater 10 and the first heat conducting member 30, and between the heater 10 and the second heat conducting member 45. The third heat conducting member 70 has a third heater side surface 70F that contacts the rear side surface 16 of the heater 10, and a third opposite surface 70R opposite the third heater side surface 70F. The first heat conducting member 30 has the first heater side surface 31 in contact with the third opposite surface 70R, and the second heat conducting member 45 has the second heater side surface 45F in contact with the third opposite surface 70R.

The third heat conducting member 70 is, for example, an anisotropic heat conducting member whose thermal conductivity in a direction parallel to the third heater side surface 70F is greater than its thermal conductivity in a direction perpendicular to the third heater side surface 70F, and an example of such a member is a graphite sheet.

The method for positioning the second thermal conductive member may also be different from that in the above embodiment.
For example, instead of the thermistor 50 having a convex portion, as shown in FIG. 9( a ), the second thermal conductive member 245 may have a convex portion 245B at both ends in the longitudinal direction, and the convex portions 245B may engage with both ends of the film 53 of the thermistor 50 .
In addition, instead of the second thermal conduction member having a convex portion, as shown in Figure 9 (b), the current interruption member 60 may have a convex portion 61A at both ends in the longitudinal direction, and the convex portions 61A may engage with both ends of the second thermal conduction member 246.
9(a), second thermally conductive member 245 may not only have convex portion 245B protruding toward thermistor 50, but also may have locking portion 345C protruding inward in the longitudinal direction from convex portion 345B, as in the embodiment shown in Fig. 9(c). Locking portion 345C engages with film 53, so that after film 53 and second thermally conductive member 345 are combined, the second thermally conductive member will not come off unnecessarily.

Also, as shown in FIG. 10, the current interrupting member 60 may be positioned to detect the temperature at a position within the range through which a sheet of the minimum width W2 usable by the heating unit 1 can pass. Even in such a case, the temperature can be accurately detected by the thermistor 50 and the current interrupting member 60. Furthermore, since the current interrupting member 60 is positioned within the range through which a sheet of the minimum width W2 usable by the heating unit 1 can pass, an abnormal temperature rise in the heater 10 can be detected regardless of the width size of the sheet.

The number of temperature detection members and current interruption members is not limited, and only one temperature detection member may be provided, or three or more may be provided. Two or more current interruption members may be provided, or none may be provided. Only the first thermistor 50A may be in contact with the second opposite surface 45R of the second heat conducting member 45. For example, the second thermistor 50B and current interruption member 60 may be in contact with the first opposite surface 32 of the first heat conducting member 30 or the back side surface 16 of the heater 10.

In the above embodiment, the first heat conducting member 30, the second heat conducting members 45 and 46, and the third heat conducting member 70 are each made of a single sheet-like member, but they may be made of a combination of multiple sheet-like members. In this case, the multiple sheet-like members may be different from each other in terms of material, thermal conductivity, shape, etc., or may be the same as each other.

In the above embodiment, the substrate 11 of the heater 10 is made of a long and narrow rectangular ceramic plate, but it may be made of a long and narrow rectangular metal plate such as stainless steel as long as it has a lower thermal conductivity than the heat conducting member 30.

In the above embodiment, the opening is a through hole formed at a position away from the contour of the heat conductive member, but it may be a notch shape.

Furthermore, the elements described in the above embodiments and variations can be implemented in appropriate combinations.

REFERENCE SIGNS LIST 1 heating unit 3 belt 10 heater 11 substrate 12 resistance heating element 13 cover 15 nip surface 16 back surface 20 holder 30 first heat conducting member 31 first heater side surface 32 first opposite surface 35A, 35B first opening 36 second opening 45 (45A, 45B) second heat conducting member 45F second heater side surface 45R second opposite surface 46 second heat conducting member 46F second heater side surface 46R second opposite surface 50 thermistor 60 current interrupting member 70 third heat conducting member 70F third heater side surface 70R third opposite surface

Claims (16)

a heater having a substrate, a resistance heating element supported by the substrate, a nip surface, and a back surface opposite the nip surface;
a temperature detection member for detecting the temperature of the heater;
an endless belt having an inner circumferential surface in contact with the nip surface and rotating around the heater;
A holder for supporting the heater;
a sheet-like first thermally conductive member located between the heater and the holder and having a thermal conductivity higher than that of the substrate, the first thermally conductive member having a first heater side surface facing the heater, a first opposite surface opposite to the first heater side surface, and an opening;
a sheet-like second thermally conductive member disposed at a position corresponding to at least the opening when viewed from a direction perpendicular to the first opposite surface, the second thermally conductive member having a second heater side surface facing the heater side and a second opposite surface opposite to the second heater side surface;
the temperature detection member is in contact with the second opposite surface of the second thermally conductive member ;
A heating unit, characterized in that, when viewed from the perpendicular direction, the second heat conducting member is smaller in size than the first heat conducting member. The heating unit according to claim 1, characterized in that the thermal conductivity from the heater to the second opposite surface is better than the thermal conductivity from the heater to the first opposite surface. The heating unit according to claim 1 or 2, characterized in that the thermal conductivity of the second thermal conductive member is greater than the thermal conductivity of the first thermal conductive member. The heating unit according to any one of claims 1 to 3, characterized in that the thickness of the second heat conducting member is smaller than the thickness of the first heat conducting member. The heating unit according to claim 1 , wherein the second heat conductive member is located within the opening. 6. The heating unit according to claim 1 , wherein a length of the first thermally conductive member in a longitudinal direction of the heater is longer than a length of the resistive heating element. A heating unit as described in any one of claims 1 to 6, characterized in that the temperature detection member detects the temperature at a position in the longitudinal direction of the heater , within a range through which a recording material of a maximum width that can be used with the heating unit can pass, and outside a range through which a recording material of a minimum width that can be used with the heating unit can pass. 8. The heating unit according to claim 1, wherein the first heat conducting member is made of aluminum or an aluminum alloy. 8. The heating unit according to claim 1, wherein the first thermal conduction member is an anisotropic thermal conduction member having a thermal conductivity in a direction parallel to the first heater side surface greater than a thermal conductivity in a direction perpendicular to the first heater side surface. a heater having a substrate, a resistance heating element supported by the substrate, a nip surface, and a back surface opposite the nip surface;
a temperature detection member for detecting the temperature of the heater;
an endless belt having an inner circumferential surface in contact with the nip surface and rotating around the heater;
A holder for supporting the heater;
a sheet-like first thermally conductive member located between the heater and the holder and having a thermal conductivity higher than that of the substrate, the first thermally conductive member having a first heater side surface facing the heater, a first opposite surface opposite to the first heater side surface, and an opening;
a sheet-like second thermally conductive member disposed at a position corresponding to at least the opening when viewed from a direction perpendicular to the first opposite surface, the second thermally conductive member having a second heater side surface facing the heater side and a second opposite surface opposite to the second heater side surface;
a third heat conducting member having a sheet shape, the third heat conducting member having a third heater side surface in contact with the back side surface of the heater and a third opposite surface opposite to the third heater side surface;
the temperature detection member is in contact with the second opposite surface of the second thermally conductive member ;
the first heat conducting member has a first heater side surface in contact with the third opposite surface,
The heating unit, wherein the second heat conducting member has a side surface of the second heater in contact with the third opposite surface. The heating unit according to claim 10, wherein the third thermal conductive member is an anisotropic thermal conductive member having a thermal conductivity in a direction parallel to the third heater side surface that is greater than a thermal conductivity in a direction perpendicular to the third heater side surface. The heating unit according to claim 11 , wherein the anisotropic heat conductive member is a graphite sheet. 13. The heating unit according to claim 1, wherein the second heat conducting member is made of aluminum or an aluminum alloy. The temperature detection member has a protrusion,
The heating unit according to any one of claims 1 to 13 , wherein the second heat conducting member is engaged with the protrusion and positioned relative to the temperature detecting member. 14. The heating unit according to claim 1, wherein the second thermally conductive member has a protrusion, and the protrusion is engaged with the temperature detection member, thereby positioning the second thermally conductive member with respect to the temperature detection member. 16. The heating unit according to claim 1, wherein the temperature detection member is a thermistor or a current interrupting member that interrupts current flow to the resistance heating element when the heater becomes abnormally hot.

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